TRACKING DOWN a friend through Brisman's cell phone led police to the e-mail address of her last client, cutting days off of investigation time, and giving them their first big clue.

The next afternoon, the mood was tense. A meeting between Brisman's family, investigators, and victim advocates was not going smoothly, following on from the awkward phone call in the early hours.

"This is our job, we feel strongly about it otherwise we wouldn't be doing it," Duff explained. "All we can do is work as hard as humanly possible to get to the end of the investigation."

The investigators had wrapped for the night at dawn and returned after three or four hours sleep. Working a big case, detectives can be on this sleep schedule for weeks.

Duff's spirits were lifted by an early morning phone call from Beth Salomonis in Denver. She and Brisman were old friends, and she'd called security at the Marriott when Brisman didn't check in last night. She seemed apprehensive, Duff said, but was willing to cooperate. She told them that Brisman had a 10 pm appointment scheduled with an "Andy M." the night she died, and gave the police Andy's phone number and e-mail address — amdpm@live.com. Duff knew that it was "remarkable" to be able to get this information so quickly. A forensic examination of Brisman's computer could've taken days.

Soon after this, a call from a District Four detective informed Duff that different numbers were used to correspond with the victims at the Westin and the Marriott, each belonging to disposable cell phones.

Duff, said Kenney, has a reputation for being good with telecommunications. And he had a theory. The suspect is shown in each photo on a cell phone. It doesn't matter that he used two different phones, each pre-paid and untraceable. Surely, there was a possibility that somewhere on his person was his real cell phone bouncing its signal off cell towers in downtown Boston?

The Boston Police Department's resident forensic data expert was on sick leave. Coincidentally though, three FBI agents were walking through the homicide unit on a completely unrelated matter.

Duff was introduced to the agents, and asked if this cell phone search was possible. One FBI agent felt it could be done, and according to Duff, opened up his computer and sat at an empty desk for hours working. Investigators began to pull cell-tower records for the time period 15 minutes before and after each incident, for those near the scene of each crime.

There were other more routine, but crucial steps to make. Boston Police officers were assigned to canvas and monitor all of the downtown hotels. Freeman supervised the autopsy at the medical examiner's office. Trisha Leffler was picked up from the Back Bay Hilton to provide fingerprints, to help police narrow their focus in the analysis of materials taken from the crime scene at the Westin. Following the autopsy, Kenney met with family to identify the body. A press conference was held that first evening and photos of the suspect were broadcast.

The investigation inched forward. On April 16, two days after the murder, it became apparent that the close proximity and downtown location of the Westin and the Marriott meant that hundreds of cell phones had likely hit on the cell towers at the time of each incident.

But a pattern was appearing.

Duff was informed by the FBI that the disposable cell phones had been used in overlapping areas of downtown, as well as the Quarry Street area of Quincy, according to his April 16 report. One of the phones had been bought at a Target in South Boston.

The district attorney also subpoenaed Microsoft, asking for account information for the amdpm@live.com e-mail address. As it turned out, the address had been set up minutes before it was used to answer Brisman's ad — and it had never been used for anything else. Microsoft supplied an IP address for where the address was created, which was linked to an area of Quincy. By the end of the day, Comcast was subpoenaed for the user information associated with the IP address. The digital crumbs were pointing investigators south of Boston.

Even without a suspect, the combination of the mounting physical and digital evidence was encouraging. But there was a new surprise in store.

At 5:30 am the next morning, April 17, Lieutenant Detective Robert Merner, the imposing, broad shouldered head of Boston homicide who bears an uncanny resemblance to Michael Chiklis from The Shield, was at home, bleary eyed, with Fox 25 on in the background. He listened, stunned, to reports of another attack in Warwick, Rhode Island, by the most wanted man in Boston.

Merner was responsible for liaising with media each day, and he knew the heat had been turned up on the investigation.

Kenney took the call from the Warwick Police Department. It was promising to see that the suspect was still active. "My biggest fear is that they've done this and now they screw the jurisdiction and never come back again," he said.

Duff's first reaction, he recalled, was something in the ballpark of disbelief. The suspect they were pursuing had his picture, albeit grainy, across state and national media, but felt comfortable striking 45 minutes out of Boston.

There was little question that they were dealing with the same suspect. The mystery man had scheduled an appointment with Cynthia Melton, an erotic dancer advertising on Craigslist. Melton was staying with her husband at a Holiday Inn Express in Warwick, on a sparingly lit strip of road adjacent to the T.F. Green Airport. The suspect had taken the stairs up to her third-floor room and pulled a gun, shaking, explaining that he was broke and needed money. He bound Melton with white flexcuffs, attempting unsuccessfully to put a ball-gag in her mouth. He was unnerved by a phone call to the room from Melton's husband, a scheduled safety precaution. When no one answered, the husband knocked on the door and the suspect escaped, gun drawn, into the hallway and down a nearby stairwell.

The suspect was again caught on camera, texting, as he left the hotel. Another disposable phone was used to contact the victim, records showed.

This piqued Duff's interest. The suspect was going to lengths to hide his identity and obscure links between the attacks, but was open about getting caught on camera, and didn't vary his outfit at each crime.

If nothing else, the Warwick incident gave detectives a third variable to plug into the cell-tower equation. And it injected a new feeling into the investigation. "When a case has motion, you know it," Kenney said.

At a meeting the following evening, the unanswered Comcast subpoena from two days previous came up. Investigators followed up and Comcast responded that they would need two weeks to turn around such a request, unless an exigency order was supplied. The district attorney's office supplied the paperwork, and with little fanfare Comcast responded immediately. At 10:30 pm on April 18, homicide investigators had on hand the name and address attached to the IP address. The digital trail had returned investigators a concrete suspect.

WAS CLARENCE SPIVEY WRONGFULLY CONVICTED OF RAPE 40 YEARS AGO? | May 11, 2012 The young woman, just 18 years old, was standing at the driver's side door of her blue Volkswagen in the parking lot of St. Joseph's Hospital in Providence on a clear and wintry Saturday evening when a young black man approached from behind and put a knife to her throat.

HUNTING THE CRAIGSLIST KILLER | April 04, 2012 Julissa Brisman's 10 pm client, her sixth and last for Tuesday, April 14, 2009, was early. She planned afterward to go out with a Yale graduate she'd met on the train to Boston the previous morning and was due back home in Brooklyn the next day.